Fundamentals of Seismic Retrofit

Earthquake engineering is applied for the seismic retrofit of structures that involves alteration of existing structures to obtain resistance to seismic activity or soil failure due to earthquakes. Retrofit is now widely performed, especially in the active seismic zones.

What Is A Seismic Retrofit?

Seismic retrofit is a field of construction engineering thatfocuses on the modification of existing structures to enhance their capability to resist earthquakes. Seismic retrofitting is achieved by the inclusion of structural improvements that may prevent the building, people, and the equipment from damage by seismic waves. In seismic zones, retrofitting may be essential for the bridges, overpasses, tunnels, and buildings, while the new construction would require compliance to seismic standards. Seismic retrofit may be executed on concrete masonry, unreinforced masonry, soft story, and concrete tilt-up construction. Soft story building is a multi-story building with abundant open space, and in concrete tilt-up construction, concrete is filled in the panels that form the walls of the structure. Since the concrete tilt-up walls are normally heavy, their seismic retrofit may be necessary. The motive for the concrete tilt-up retrofit is to prevent the separation of the roof from the building walls.

Categories of Seismic Retrofit

There are several categories of seismic retrofit, and their nature depends upon the purpose for which retrofit is executed. The main form is the public safety retrofit that involves structural reinforcement to save human life (though some degree of injury is acceptable). Such retrofit is performed on structures that are not extremely expensive and for which a complete rebuild is not desired. A lower level retrofit may be selected to ensure earthquake endurance of the structure with some repairs needed after the earthquake. Extensive retrofit may be essential for the buildings that are important due to cultural, historical, or other reasons. Mostly, retrofit is performed on buildings that are extensively high, with an unsafe earthquake vibration frequency. Roads also have a priority in retrofit because their serviceability is essential during an earthquake to ensure the functioning of the emergency services.

Seismic Retrofit Measures

There are numerous techniques that are being used for the retrofit of structures, and their selection is based on the objective of retrofit, type of structure, soil conditions, and the expenditures involved. Retrofitting of buildings may reduce the earthquake damage by suitable structural modifications, but no technique will completely eliminate the risk of seismic waves. Reinforcement of the buildings by the use of girders and trusses is normally implemented to make the buildings safe. Base isolators are utilized to decouple the structure from the shaking ground, thus achieving seismic vibration control. Supplementary dampers minimize the structure resonant effects, increase the energy dissipation, and reduce the displacement of structures. Other retrofit techniques include the use of absorbers and baffles to make a building safe from an earthquake.